1. Field of the Invention
The present invention relates to couplings for connecting between pipes and container valves comprising a first piece provided on the container valve and having a seal surface and a screw portion, a second piece having a seal surface, a screw member which is screwed into the screw portion of the first piece and turned to press the seal surface of the second piece against the seal surface of the first piece so as to hermetically seal and connect the first and second pieces.
2. Prior Art
In an industrial field of semiconductors such as ICs and LSIs, the semiconductors are manufactured in a clean room excluding fine particles, and hence the environment and conditions for manufacturing the ICs, etc. are very severe. A special gas used in the manufacturing operation is introduced into a clean room through a pipe from the outside of the clean room, thereby preventing such special gas from mixing with other undesired molecules of gas such as air.
Accordingly, couplings for connecting between pipes and container valves as well as connecting between the pipes require very high accuracy thereof. Further, couplings for use in high pressure gas containers, etc. require complete sealing for safety reasons thereof.
Accordingly, to meet these requirements in the coupling for connecting between a pipe and a container valve, the JIS standard in Japan and the CGA (Compressed Gas Association) standard in has been set in the U.S.A.
A conventional coupling for connecting between a pipe and a container valve manufactured in accordance with the CGA standard is shown in FIG. 4.
In the same figure, denoted by 10 is a first coupling piece serving as one piece provided on the container valve (not shown), 20 is a second coupling piece (nipple) serving as another piece, and 30 is a nut member serving as a screw member.
The first coupling piece 10 includes a screw member 11 (a female screw portion 11 in FIG. 4) integrally formed therein, and a seal surface 15 formed at the innermost part thereof, namely, at the portion located inwardly of inner than the female screw member 11. The seal surface 15 is formed as a tapered hole so as to be brought into contact with a seal surface 25 of the second coupling piece 20.
The second coupling piece 20 includes a retaining portion 21 and the seal surface 25 is formed on this retaining portion 21. The seal surface 25 is formed as a tapered outer peripheral surface of the retaining portion 21. The second coupling piece 20 is hermetically attached to a pipe 2.
The screw or nut member 30 includes a male screw portion 31, which is formed on the outer peripheral surface at the tip end thereof and screwed into the female screw portion 11 of the first coupling piece 10 and turnable relative to the female screw portion 11, and a through hole 32 which is provided on the inner peripheral surface and the second coupling piece 20 can be engaged in the through hole 32 and movable along the axial direction of the through hole 32. The nut member 30 has a pressure surface 33 which is formed at the tip end surface thereof and is capable of pressing a rear end 23 of the retaining portion 21 of the second coupling piece 20.
The first coupling piece 10, the second coupling piece 20 and the nut member 30 are respectively made of metal such as stainless steel and brass.
When the male screw portion 31 of the nut member 30 at the side of the second coupling piece 20 is turned while it is screwed into the female screw portion 11 of the first coupling piece 10, the pressure surface 33 presses the second coupling piece 20 against the first coupling piece 10 so that both seal surfaces 15 and 25 are pressed against and brought into contact with each other. As a result, the first and second coupling pieces 10 and second coupling piece 20 are sealed hermetically and connected with each other.
There is a likelihood of occurrence of a case in the coupling for connecting between a pipe and a container valve that the second coupling piece 20 is turned together with the nut member 30 when the nut member 30 is turned to tighten the first and second coupling pieces 10 and 20 along the axial direction thereof so that the seal surface 25 is turned while it is brought into contact with the seal surface 15.
If such a case occurs, the seal surfaces 15 and 25 are liable to be scratched, and when such scratched first and second coupling pieces 10 and 20 are repeatedly used, there is a possibility of impairment of the sealing property and of leakage of gas such as poisonous gas in the pipe. Further, when the metallic seal surfaces 15 and 25 are scratched relative to each other, there is a possibility of generation of particles and of entrance of these particles into the pipe. Still further, when the first and second coupling pieces 10 and 20 which are scratched on their seal surfaces 15 and 25 are recycled, it is necessary to tighten the nut member 30 stronger to prevent the leakage of gas, thereby reducing the workability.
Even if the first piece is formed of the second coupling piece 20 or the second piece is formed of the first coupling piece 10, the same problems occur.